1. Field of the Invention
The present invention relates to a method for preparation of dialkylnaphthalenes, especially 2,6-dialkylnaphthalene and a catalyst for the use.
2. Description of the Prior Art
In Japanese patent publication Tokkosho No. 56-2532, there has been proposed a method for preparation of beta-isopropylnaphthalene comprising: reacting naphthalene with propylene in the presence of a solid acidic catalyst such as silica, alumina or zeolite, subsequently collecting diisopropylnaphthalene fraction by distillation, separating 2,6-diisopropylnaphthalene from the fraction by crystallization and forming beta-isopropylnaphthalene by transalkylation between naphthalene and 2,6-diisopropylnaphthalene. But such solid acidic catalyst is not satisfactory from the viewpoint of transalkylation activity, isomerization activity and lifetime of the catalyst in the preparation of dialkylnaphthalenes. (cf. Comparative Examples 1, 3, 4, 8, 9 and 10 described below)
In Japanese patent publication Tokkosho 42-3617, there has been proposed a method of olefin-alkylation of an aromatic hydrocarbon at 1-200 atm. and 210.degree.-325.degree. C. in the presence of a catalyst composed of a fire-proof inorganic oxide selected from a group of alumina, silica, silica-alumina, silica-alumina-magnesia, silica-magnesia, silica-zirconia, alumina-zirconia, alumina-boria, zirconium dioxide and titanium dioxide, which contains 2-12 weight percent, preferably 2-8 weight percent of fluorine, with Hammett's reaction constant of -8.0 or less and is calcined at 450.degree.-700.degree. C. in an inert gas substantially free of water and oxygen, and a method of transalkylation of the alkylaromatic hydrocarbon at 1-200 atm. and 220.degree.-350.degree. C. Alkylation and transalkylation of single-ring aromatic hydrocarbons only were described as examples, but naphthalene and alkylnaphthalenes were referred as aromatic hydrocarbons therein.
However, neither all of above-mentioned inorganic oxides containing fluorine are always suitable as the catalyst for preparation of dialkylnaphthalenes by alkylation of naphthalene and/or a monoalkylnaphthalene with an olefin (cf. Comparative Examples 5, 6 and 7 described below), nor suitable reaction conditions for the preparation of dialkylnaphthalenes were mentioned in it.